recent upturn in use in 1993 was accompanied, and even preceded, by a downturn in perceived risk.
The MTF study also measures perceived availability of alcohol, cigarettes, or illicit drugs, but analyses of that data did not show changes in perceived availability that could account for the changes in use. Without such data and analyses, the declines in marijuana and cocaine use might have been attributed to putative successes in reducing availability. Thus, the epidemiological data provide a means to generate hypotheses and also to refute hypotheses.
Epidemiological data can also be used to address more fundamental issues having to do with ''norms" related to illicit drug use.13 Epidemiological research can be very useful in assessing what the norms are for particular drug-related behaviors and how those norms vary by person, place, and time. Most researchers in the field would emphasize the role of social factors, including broad social-cultural norms, in influencing initiation and experimental use of alcohol, tobacco, or illicit drugs, while intraindividual factors (biological and psychological) would be emphasized in influencing the transition to abuse or dependence (Glantz and Pickens, 1992). Epidemiological research in this field continues to go beyond descriptive documentation of occurrences of a condition according to persons, place, and time by contributing causal analyses of the occurrences.
The patterns, prevalence, and consequences of alcohol, tobacco, and illicit drug use and abuse within youth populations are not fully understood. As mentioned above, young African Americans have significantly lower levels of cigarette and illicit drug use than most of their peers. The 1993 MTF study found that 4.9 percent of African American high school seniors reported daily cigarette use, compared with 22.9 percent of white students (Johnston et al., 1995). The reasons for those differences are not yet understood, and it would be useful to elucidate the reasons for low use among African Americans to determine if that information could be transferred across cultural lines. Further, ethnographic research could provide important data on local-level illicit drug use that could be used to identify potential trends; study the natural history and progression of alcohol, tobacco, and illicit drug use; and provide greater detail than more quantitative surveys.
Studying the problem of illicit drug use and abuse in a variety of